conditional-statements | 易学教程

How to install features depending on the value of property

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I have a registry key that can be equal to one of two values: special value or null . And two features. When my registry key equals to special value the installer has to install first feature. if registry key is not found by registry search the installer has to install second feature. And if registry key has null value the installer must not install any of these two features. What I'm doing or understanding wrong? If INSTALLLEVEL=5, SPECIALVALUE="special",MYTREAT="1" the first feature must be installed,but the installer doesn't install both of the features in this case. <Feature Id="MyFeatures

C++: Set bool value only if not set

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I have code in my C++ application that generally does this: bool myFlag = false; while (/*some finite condition unrelated to myFlag*/) { if (...) { // statements, unrelated to myFlag } else { // set myFlag to true, perhaps only if it was false before? } } if (myFlag) { // Do something... } The question I have pertains to the else statement of my code. Basically, my loop may set the value of myFlag from false to true, based on a certain condition not being met. Never will the flag be unset from true to false. I would like to know what statement makes more sense performance-wise and perhaps if

What is condition synchronization?

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问题 Could someone explain condition synchronization to me? An example (preferably in C#) would be greatly appreciated also. 回答1: It sounds like your professor is talking about threading. Threading enables computer programs to do more than one thing at a time. The act of starting a new thread while one is already running is called "spinning up a thread" by computer programmers. Threads can share the same memory space. Condition Synchronization (or merely synchronization) is any mechanism that

Assign class boolean value in Python

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If statements in Python allow you to do something like: if not x: print "X is false." This works if you're using an empty list, an empty dictionary, None, 0, etc, but what if you have your own custom class? Can you assign a false value for that class so that in the same style of conditional, it will return false? You need to implement the __nonzero__ method on your class. This should return True or False to determine the truth value: class MyClass(object): def __init__(self, val): self.val = val def __nonzero__(self): return self.val != 0 #This is an example, you can use any condition x =

How to evaluate the constants SymPy gives with initial condition?

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How can I evaluate the constants C1 and C2 from a solution of a differential equation SymPy gives me? There are the initial condition f(0)=0 and f(pi/2)=3. >>> from sympy import * >>> f = Function('f') >>> x = Symbol('x') >>> dsolve(f(x).diff(x,2)+f(x),f(x)) f(x) == C1*sin(x) + C2*cos(x) I tried some ics stuff but it's not working. Example: >>> dsolve(f(x).diff(x,2)+f(x),f(x), ics={f(0):0, f(pi/2):3}) f(x) == C1*sin(x) + C2*cos(x) By the way: C2 = 0 and C1 = 3. There's a pull request implementing initial/boundary conditions, which was merged and should be released in SymPy 1.2. Meanwhile, one

IE Conditional operator: OR … if is greater than ie9 or not IE

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I want to only include history and ajaxify if the browser is ie9 or greater, OR is not ie:  How can I use the OR operator to say this:  <script type="text/javascript" src="assets/js/plugins/history.js"></script> <script type="text/javascript" src="assets/js/plugins/ajaxify.js"></script> <![endif]--> Yeah, the or operator is: | . You

switch statement in Jquery and List

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I would like to know if my approach is efficient and correct. my code is not working though, I don't know why. <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js" type="text/javascript" charset="utf-8"></script> <script type="text/javascript"> $(document).ready(function() { function HotelQuery(HotelName) { switch (HotelName) {

complex IF statement in assembly

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问题 How should I write such an if statement in assembly? if ((a == b AND a > c) OR c == b) { ... Platform: Intel 32-bit machine, NASM syntax. Update For variable types and value, use whatever is more easy to understand. Integers would works fine for me, I guess. 回答1: In generic assembly, it will be basically something like this ( a in ax , b in bx , c in cx ): cmp bx, cx jeq istrue cmp ax, cx jle isfalse cmp ax, bx jeq istrue isfalse: ; do false bit jmp nextinstr istrue: ; do true bit nextinstr:

How to use conditions in features in WiX?

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问题 I am trying to make simple Windows intaller, and I don't know how to deal with this. I have two features - feature1 and feature2. I want feature2 to be installed only if the user selected feature1 to be installed. So I tried: <Feature Id='core' Title='Core' Description='ØMQ 1.0.0 core functionality and C++ API' Level='1'> <ComponentRef Id='Core_include' /> <ComponentRef Id='Core_bin' /> <ComponentRef Id='Core_lib' /> <ComponentRef Id='Core_zmq' /> <ComponentRef Id='cpp_bin' /> </Feature>

Conditional Statements in PHP code Between HTML Code

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问题 I'm having a bit of an issue by using Conditional Statements in PHP separated by HTML code. This is the type of code I'm trying to write. This is a profile page and it should only be seen by the user whose profile it is (i'm using session variables for checking that) : <?php if(check if user is logged in) ?> <display users profile in html> <?php else ?> <display an error> But this doesn't work. I also tried using the shorthand notation by putting a : at the end of the if and using the endif